Jaw-Dropping Similarity Found in Whales and Pelicans

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One of the more surprising features of nature is the ability of
two unrelated animals to independently evolve extremely similar
body parts. In a new study, scientists demonstrate that rorqual
whales — whose members include the largest animal on Earth, the
blue whale — have come to share very similar feeding mechanisms
and jaw structures with pelicans, despite clearly independent
pathways of evolution.

"You can have two organisms that are as completely different as a
pelican and a rorqual whale are — you just have to look at them
to immediately understand the differences — but, that said, they
have these extraordinary similarities as well," said study leader
Daniel Field of Yale University. The finding, he said, was the
exciting result of a computer program he and his research team
designed to examine bone strength.

Basically they take advantage of stretchy tissue between their
jaws to open up their mouths incredibly wide and let in huge
rushes of water, hopefully filled with fish and other prey.

"This tissue is so stretchy that rorquals can increase their body
volume by up to 50 percent during a feeding event, which is
really remarkable because 50 percent of the largest animal on
Earth is really huge," Field told LiveScience. And pelicans can
increase their total body volume by up to 300 percent.

A strong lower jaw, one able to withstand the high drag forces
encountered during engulfment feeding, independently evolved in
both species.

When two animals arrive at the same endpoint — in this case,
these similar feeding structures — via different processes, it's
called
convergent evolution.

To test just how similar the jaws of rorqual whales and
pelicans are, the researchers designed a special computer program
that can assess a bone's ability to resist bending, based on data
from CT scans.

"We feel that the computer program is pretty important in its own
right," Field said. "It enables scientists to study a bone's
bending resistance without damaging rare specimens."

The researchers found that the jaws of both species exhibit the
exact same pattern of bending resistance.

"The really interesting implication was the realization that what
we had was a pretty textbook example of convergent evolution,"
Field said. "You have two unrelated animals contending with
really similar selective pressures, which forces them to adopt
similar adaptations."

Bats and birds

Convergent evolution, while sometimes startling, is not that
rare. Whenever two organisms are exposed to similar environmental
pressures, such as the challenges of finding prey in the ocean,
or even the dryness of a desert, they sometimes end up developing
similar ways of coping.

A famous example is wings. Both bats, which are mammals, and
birds, which are thought to have evolved from dinosaurs, have
wings that enable them to fly. Yet the animals otherwise have
little in common. They did not evolve from a common ancestor with
wings, but instead arrived at wings on their own. [ Galleryof
Colorful Wings ]

"They evolved similar adaptations for flight, but they did it in
totally different ways," Field said. "Convergent evolution is
something really prevalent not just in animals but in biology in
general."

Learning more about examples of convergent
evolution in new organism pairs, such as the rorqual and the
pelican, offers scientists a hope of better understanding of the
intricacies of evolution.

"To get an example of convergent evolution that is so directly
similar, with such close parallels in the feeding apparatus in
really different organisms — it's a really compelling example
that has the potential to show you how evolution proceeds," Field
said.

The new study will be published in the July edition of the
journal The Anatomical Record.

You can follow LiveScience.com senior writer Clara Moskowitz
on Twitter @ClaraMoskowitz.
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